EP4433342A1 - Device for adjusting the clamping force of an electromechanical brake - Google Patents

Abstract

The clamping strategy of an electromechanical brake is dependent on existing hydraulic pressure to adjust the mechanical component of the clamping force and prevent excessive brake clamping. The hydraulic component (Fhyd) of the clamping force is estimated from a pressure measurement, subtracted from a target force (FTar), to produce the mechanical component to be applied (FTarNew) and the electric motor for controlling the brake clamping is stopped at a threshold value (I2) of the current that is supplied thereto according to the value of said mechanical component to be applied.

Description

Description

Title: Clamping force adjustment device for an electromechanical brake

The invention relates to a clamping force adjustment device for an electromechanical brake.

Many vehicles include electromechanical brakes for at least some of their wheels. Such brakes can be used as parking brakes, but also as service brakes during movement of the vehicle and as emergency brakes in special circumstances. When they are used as a service brake, the braking that they impose depends on the pressure on the brake pedal by the driver and the hydraulic pressure that he then applies. In parking brake and emergency brake circumstances, an engine control unit automatically applies brake application strategies, predefined according to various parameters of the state or driving of the vehicle, by imposing application movements to a brake actuator, by starting an electric motor.

Many tightening strategies consist of applying a tightening force determined by the continuous measurement of the electric current that it is necessary to apply to the electric motor to continue the tightening movement. The disadvantage of this simple strategy is that it does not take into account the hydraulic pressure which may already be present in the brake and exerts a preliminary clamping force. The force applied by the strategy is then added to this preliminary force, and the total force obtained when the strategy stops exceeds the force required to guarantee tightening: the excessive tightening (“overclamping”) which is reached has the inconvenience of prematurely wearing out the brake by stressing it too strongly, while needlessly consuming energy for the application, then for the release which will follow later.

An object of the invention is therefore to avoid excessive application of electromechanical brakes by blindly applying a strategy independent of a hydraulic pressure already present in the brake.

It is precisely sought to obtain as much as possible a final tightening force which is invariable, independently of the hydraulic pressure applied at the start. Another object of the invention is to estimate and to put in relation of calculation the two components of hydraulic and mechanical force which take part together in the application of the brake, although they depend on physical phenomena and on heterogeneous mechanisms, and are obtained from measurements and calibrations which may be imprecise, in order to obtain despite this the result, mentioned above, of an almost invariable final tightening force, with satisfactory precision.

Yet another object of the invention is to ensure the maintenance of a sufficient clamping force, even in circumstances where the hydraulic pressure will not be maintained, due to a relaxation of the support of the brake pedal. by the driver.

According to a first general aspect, the invention relates to a motor control unit intended to control an electric actuator motor of an electromechanical vehicle brake, comprising:

- a module for supplying commands to the electric motor, including brake application commands;

- a module for continuous measurement of values of an electric current supplied to the electric motor during tightening commands;

- A module for measuring hydraulic pressure applied to the brake;

- and a decision module, designed to control the command supply module according to predefined strategies, the strategies comprising, for the tightening commands, stopping the tightening at a target tightening force applied by the brake, the stopping being decided by the decision module according to the measurements of the values of the electric current according to the measurement of the hydraulic pressure.

In the invention, the mechanical component of the mechanical clamping force applied by the brake is correlated to the value of the current necessary for the electric motor moving the brake actuator, and the clamping is stopped when the sum of the mechanical component and the hydraulic tightening component, estimated thanks to the pressure measurement, reaches a target value defined by the strategy.

According to a second general aspect, the invention relates to an electromechanical brake device for a vehicle, comprising said brake, which is associated with a wheel of the vehicle, an actuator of the brake, said electric motor of the actuator, and the preceding electric motor motor control unit.

According to certain optional improvements of the invention: the decision module is designed to estimate a total clamping force applied to the brake by adding a first component depending on the values of the electric current and a second component depending on an estimate of the hydraulic pressure;

the hydraulic pressure measurement is made at a master cylinder of the vehicle;

the estimate of the estimated hydraulic pressure is equal to the measurement of the hydraulic pressure reduced by a fixed value;

- the fixed value is 7 to 15 bars;

- the fixed value is 10 bars;

the second component is proportional to the estimate of the hydraulic pressure, by applying a reduction coefficient to said estimate of the hydraulic pressure;

- the reduction coefficient is fixed and between 15% and 30%;

- the reduction coefficient is 20%;

- the decision module is designed to estimate the second component, then estimate a value of the first force component for which the tightening force will be equal to the target tightening force, and stop the command providing module when a threshold of the electric current, estimated as corresponding to said value of the first force component, is measured.

Another object of the invention is a vehicle provided with an electromechanical brake device according to the above.

The invention will now be described in its various aspects, characteristics and advantages by means of the following figures, which illustrate a preferred embodiment thereof, given purely by way of illustration.

- Figure 1 schematically shows a motor vehicle;

- Figure 2 illustrates a brake comprising an exploded parking device;

- Figure 3 illustrates the motor control unit of said brake;

- Figure 4 illustrates the progress of a known strategy applying a component of mechanical force of uniform value for the application of an electromechanical brake; - Figure 5, another progress of this known strategy;

- Figure 6 illustrates a flowchart of the brake application method according to the strategy of the invention;

- Figure 7, the progress of a strategy according to the invention;

- And Figure 8 is a diagram of a hydraulic brake circuit.

FIG. 1 represents an automobile 1 equipped with two driving and steering front wheels 2 on a front axle 3, and two non-driving and non-steering rear wheels 4 on a rear axle 5. Each of the front wheels 2 is here equipped with a service brake 6 actuated directly by the driver by pressing a brake pedal, and each of the rear wheels 4 is equipped with a brake 7 described below in detail, and which is associated with an actuator 8 able to make it work in parking and emergency brake. The actuators 8 of the two brakes 7 are controlled by the same engine control unit 9 according to various information relating to certain parameters of the vehicle 1 and its driving state. The engine control unit 9 is active when emergency braking becomes necessary or parking is requested. For the hydraulic service braking functions, the brakes 7 are also actuated by the driver at the same time as the brakes 6 at the front.

Figure 2 schematically illustrates a known and non-limiting embodiment of the brake 7, according to an exploded view. The brake 7 comprises a caliper 11 joined to a casing 12 of cylindrical shape. It also includes a gearmotor 60, one flange 61 of which is joined to a flange 62 on the rear face of the casing 12 by screws (not shown here). The geared motor 60 contains an electric motor 18 and gears for reducing the rotational speed of said electric motor 18. The housing 12 comprises a hydraulic cavity 13 called a cylinder, open towards the front (on the right in FIG. 2) and in which slides a piston 14 carrying a movable pad (not shown). Braking is carried out by causing the piston 14 to slide forwards, to bring the movable pad closer to a fixed pad located at the front end of the caliper 11 and grip a disc of the rear wheel 4 between these pads. This movement of the piston 14 is obtained, when the brake 7 works as a service brake, by the application of hydraulic pressure in the hydraulic cavity 13 while driving the vehicle: this pressure is exerted on the rear face of the piston 41 and pushes him forward. If, however, brake 7 is controlled as a parking brake or an emergency brake, the braking is carried out by the use of the electric motor 18 according to strategies imposed by the motor control unit 9. The electric motor 18 sets in motion the gears of the geared motor 60, which causes a screw 15 which extends in the hydraulic cavity 13. The screw 15 engages with a nut 16 on which a rear face of the piston 14 is then in abutment. The rotations of the screw 15 are converted into translations of the nut 16 and of the piston 14, which moves according to the duration of actuation of the electric motor 18. The actuator 8 considered here comprises in particular the geared motor 60 and therefore its electric motor 18, and the system 17 made up of screw 15 and nut 16.

The invention could be applied to other vehicles and other brakes than these.

Figure 3 illustrates the motor control unit 9 in more detail: it comprises: a command supply module 19 which supplies commands to the electric motor 18 according to the predefined strategies, being connected to a battery or another source of energy present in the vehicle 1; a current measurement module 20 which measures the intensity of the current in the electric circuit on which the electric motor 18 and said energy source are installed; a pressure measurement module 21 which measures hydraulic pressure in the braking system; and a decision module 23 which connects the command supply modules 19 and measurement modules 20 and 21, and which uses the output signal of the measurement modules 20 and 21 to adjust the duration of the commands.

Reference is made to FIG. 4. It illustrates a diagram 30 of the electric current I applied to the electric motor 18, and a diagram 31 corresponding to the clamping force F of the brake 7 during the known strategy, as a function of time t, and in the absence of hydraulic pressure in the brake 7. The current diagram 30 comprises three successive portions: a starting peak 32, a flat portion 33, and an increasing portion 34.

The starting peak portion 32 begins from the instant ti of application of the strategy, has a short duration and a high value; it corresponds to the starting of the motor and does not produce tightening.

The flat portion 33, of relatively long duration, corresponds to an empty stroke of the piston 14 before the tightening actually begins and is carried out at a nearly constant and low value of the current I from a time t?. And the increasing portion 34 begins at a time ts and has a roughly uniform slope with time. It corresponds to a gradual increase in the clamping force F, or its mechanical component.

The force diagram 31 comprises a portion of zero (or negligible) force 35, then a portion of increasing force 36 starting at a time t4 simultaneous or almost simultaneous with time t3. The growth of the clamping force F has an almost invariable slope in this growth part 36, so that the clamping force can, at least approximately, be correlated to the value of the current I by a proportionality relationship . The tightening strategy is stopped when an intensity threshold li of the current I, correlated to a target force F _Tar of the tightening, is reached. The clamping force F varies very little thereafter.

If now the known strategy is applied while a hydraulic tightening already exists, its sequence is as follows according to Figure 5. The current diagram, now 40, still has a starting peak portion 42, a flat portion 43 and a growing portion 44, similar to the previous ones, except that the durations of the flat portion 43 and of the growing portion 44 may be different. As before, the increasing portion 44 is interrupted at the intensity threshold 11, identical to the previous one, of the current I.

But the force diagram, now 41, starts at a non-zero Fhyd value because of the hydraulic pressure. It remains constant during a flat portion 43 of the diagram, then increases during an increasing portion 46 which begins approximately at the same time as the increasing portion 44. Its slope is approximately the same as in Figure 4, so that the force exceeds, possibly by a great deal, the target force F _Tar at the end of the strategy, which corresponds to excessive tightening (“overclamp”) harmful to the duration of the brake and to the correct operation of the vehicle 1 in general .

The strategy modified according to the invention is shown schematically in FIG. 6. A first step is a decision (E50) to apply the tightening strategy, and the motor is started (E51). There follows a step of measuring the hydraulic pressure (E52), a step of correcting the measurement (E53), and a step of calculating the hydraulic component of force Fhyd already applied to the brake 7 (E54); then a step of calculating the mechanical component of force to be applied FTarNew (E55), a step of estimating (E56) the final value of the current necessary to establish this mechanical component (modified threshold h of current intensity). The measurements of the electric current (E57) are taken immediately after tightening has been decided, and they are compared (E58) with the final value determined in step E56. The strategy is continued as long as the values of the repetitive current measurements remain below the modified threshold I2, and interrupted when the current measurement values reach this threshold. The motor is then stopped (E59).

In the absence of an initial hydraulic pressure resulting from service braking of the wheel of the vehicle, the parking braking strategy by the electromechanical brake proceeds identically to that of FIG. 4. If, on the contrary, a hydraulic pressure , in particular constant or at least not increasing, is already applied following service braking, FIG. 7 shows that the current diagram 40 is replaced by a current diagram 63 which differs in that the increasing portion, now 64, is shorter by stopping at the modified threshold I2, lower than li, calculated in step E55. The corresponding force diagram 65 likewise comprises an increasing portion, now 66, shorter and which stops near the target force Fyar (unchanged with respect to the known strategy), since the mechanical component of the clamping force , for wheel parking braking, has been reduced by a value corresponding as far as possible to the existing hydraulic component. This hydraulic component FHyd is maintained for a flat portion 67, corresponding to the flat portion 45, of the force diagram 61.

Here are now the rules applied in this particular embodiment of the invention to improve the precision of the clamping force or to make the modified strategy perfectly safe.

FIG. 8 represents a hydraulic braking circuit, comprising a master cylinder 70, a pressure amplifier, a pump or any other source of pressurized brake fluid, in communication by a network 71 of pipes with the cylinders 13a to 13d of the brakes 6 and 7, electromechanical or not, fitted to the wheels 2 and 4 of the vehicle 1. It is preferred that the existing hydraulic pressure be measured at the master cylinder 70 rather than at the cylinders 13a to 13d, because it can be estimated with greater precision. big.

A correction of the measured value P _{me s} is applied to take into account the uncertainties of the measurements. It can be, for conventional braking systems where the hydraulic pressure can reach approximately 150 bars (15 MPa), from 7 to 15 bars (0.7 to 1.5 MPa), and for example 10 bars (1 MPa). The measured value Pmes is reduced by this value, in order to not to overestimate the hydraulic component of the tightening force and to guarantee sufficient final tightening. This correction value is denoted P _CO rr.

It is also necessary to guard against subsequent decreases in the hydraulic pressure, if in particular the brake pedal were released. It was found that the pressure loss would then be moderate. A reduction coefficient K _CO rr of between 15 and 30% (between 0.15 and 0.30 in the formula below), and for example around 20%, can be applied.

An estimated pressure P _es t is then obtained, by means of which the hydraulic force FHyd is calculated, according to the following formula:

P is ⁼ (P mes P corr), and the hydraulic force component can be estimated by the formula: in which is the diameter of the piston 14.

The required mechanical component FïarNew to obtain the target tightening force Fï _ar is given by the following formula:

FïarNew ⁼ Fïar Fhyd, and the value of the modified threshold l ₂ at which the strategy is stopped can be obtained by a formula such as:

I? = I l . ( FïarNew / Fïar ), possibly adjusted according to the characteristics, obtained empirically, of the behavior of the brake 7 and the actuator 8.

The invention can be implemented in different ways: the correction or reassessment calculations of the hydraulic pressure applied and of the mechanical component of force to be applied could thus be done according to an order different from that of steps E53 to E56. The hydraulic pressure measurement can be made with an already existing sensor on the vehicle 1, and may or may not be renewed during the application of the strategy.

Nomenclature

1 Automotive

2 front wheels

3 Front axle 4 rear wheels

5 Rear axle

6 Brake

7 Electromechanical brake

8 Actuator

9 Engine control unit

11 Caliper

12 Housing

13, 13a to 13d Cylinder

14 Plunger

15 Screws

16 Nut

17 Screw-nut system

18 Electric motor

19 Order Delivery Module

20 Current measurement module

21 Pressure measurement module

23 Decision module

30 Current diagram

31 Stress diagram

32 Boot Peak

33 Flat Portion

34 Growing Portion

35 Flat Portion

36 Growing Portion

40 Current diagram

41 Stress Diagram

42 Boot Peak

43 Flat Portion

44 Growing Portion

45 Flat Portion

46 Growing Portion 60 Gearmotor

61 Bridle

62 Bridle

63 Current diagram

64 Growing Portion

65 Stress diagram

66 Growing Portion

67 Flat Portion

70 master cylinder

71 Pipe network

E50 Tightening decision

E51 Power on

E52 Pressure measurement

E53 Fix

E54 Hydraulic component

E55 Mechanical component

E56 Current threshold

E57 Current measurement

E58 Threshold reached?

E59 Stop

F Clamping force

FHyd Hydraulic force component

Fïar Tightening target force

FïarNew Target Mechanical Component

I Electric current intensity

11 Stop threshold

12 Modified stop threshold

Kcorr Correction factor

P _mes Pressure measured

P corr Correction pressure

P is Estimated Pressure t1 to t5 Instants of time diagrams t Time

Claims

1. Motor control unit (9) configured to control an electric motor (18) of an actuator (8) of an electromechanical brake (7) of a motorized vehicle during braking of a wheel of the motorized vehicle, comprising: - a module for supplying commands (19) to the electric motor, including brake application commands; - a continuous measurement module (20) of values of an electric current (I) supplied to the electric motor during tightening commands; - a measurement module (21) of a hydraulic pressure applied to the brake; - and characterized in that it further comprises a decision module (23), designed to control the command supply module (19) according to predefined strategies, the strategies comprising, for the tightening commands, a stop of the clamping to a target clamping force (Fiar) applied by the brake, the stopping being decided by the decision module according to the measurements of the values of the electric current as a function of the measurement of the hydraulic pressure, in which the module decision is designed to estimate a total clamping force applied to the brake by adding a first electromechanical component (FtarNew) depending on the values of the electric current and a second hydraulic component (FHyd) depending on an estimate of the hydraulic pressure (Pest), the decision module (23) being designed to estimate the second hydraulic component (Fnyd), then to estimate a value (FiarNew) of the first electromechanical force component for which the tightening force will be equal to the target tightening force (Fiar), and stopping the command supply module (19) when a threshold (U) of the electric current, estimated as corresponding to said value of the first electromechanical component of effort, is measured. 2. Electromechanical brake device for a vehicle, comprising said brake (7), which is associated with a wheel (4) of the vehicle, an actuator (8) of the brake, said electric motor (28) of the actuator, and the motor control unit (9) of an electric motor according to claim 1. 3. Brake device or engine control unit according to claims 1 to 2, characterized in that the hydraulic pressure measurement is made at a master cylinder (70) of the vehicle. 4. Brake device or engine control unit according to claims 1 to 3, characterized in that the estimate of the hydraulic pressure (P _es t) estimated is equal to the measurement of the hydraulic pressure (Pmes) reduced by a fixed value (P _CO rr). 5. Brake device or engine control unit according to claim 4, characterized in that the fixed value is 7 to 15 bar. 6. Brake device or engine control unit according to claims 3 and 4, characterized in that the fixed value is 10 bar. 7. Brake device or engine control unit according to claim 1, characterized in that the second hydraulic component is proportional to the estimation of the hydraulic pressure (Pmes), by applying a reduction coefficient (K _CO rr) to said estimation of hydraulic pressure. 8. Brake device or engine control unit according to claim 7, in that the reduction coefficient is fixed and comprised between 15% and 30%. 9. Brake device or engine control unit according to claim 8, characterized in that the reduction coefficient is 20%. 10. Brake device or engine control unit according to any one of the preceding claims, configured in that the second hydraulic component does not increase during braking, the second hydraulic component preferably being substantially constant during braking. 11. Brake device or motor control unit according to any one of the preceding claims, in which the electromechanical brake is a parking brake, the control unit being a motor control unit configured to control parking braking of the wheel. 12. Brake device or engine control unit according to the preceding claim, in which the second hydraulic component is a hydraulic component which results from a previous service braking of the wheel, the engine control unit controlling the electromechanical brake the first electromechanical component for wheel parking braking. 13. Brake device or motor control unit according to any one of the preceding claims, in which the electromechanical brake is an electromechanical brake and not hydraulic, the motor control unit being configured to control electromechanical braking of the wheel by the first electromechanical component 14. Brake device or motor control unit according to any one of the preceding claims, in which the decision module (23) is designed to carry out a braking control method consisting of the following steps successively and in this order: estimation of the second hydraulic component (Fnyd), then estimation of a value (FTarNew) of the first electromechanical force component for which the tightening force will be equal to the target tightening force (Fïar), and stoppage of the provision of commands (19) when a threshold (I2) of the electric current, estimated as corresponding to said value of the first electromechanical force component, is measured. 15. Motor vehicle, characterized in that it is provided with an electromechanical brake device according to any one of claims 2 to 14.